Conventionally, there is well known a rotary atomizing head or a rotary atomizing coating machine having a rotary atomizing head. The rotary atomizing head is a cup-like or trumpet-like member which is called bell cup. Paint supply holes are formed in the inner peripheral surface of the rotary atomizing head so as to supply paint. The paint supply holes are normally circular holes or oval holes and are arranged circumferentially so that the distance between each paint supply hole and the center of the inner peripheral surface of the rotary atomizing head is substantially equal to each other. The rotary atomizing head applies centrifugal force on the paint supplied to the inner peripheral surface by rotating itself so as to discharge the paint outside atomizingly.
Such a rotary atomizing head is disclosed in the Japanese Patent Laid Open Gazette Hei. 9-220498, the Japanese Patent Laid Open Gazette Hei. 8-84941 and the Japanese Patent Laid Open Gazette Hei. 3-101858 for instance.
However, when the rotary speed of the rotary atomizing head is increased or viscosity of paint is high, paint supplied to the inner peripheral surface of the rotary atomizing head is moved within quite shallow parts on lines connecting the paint supply holes to the corresponding points on the peripheral edge of the inner peripheral surface, and is not spread on the inner peripheral surface of the rotary atomizing head uniformly. As a result, when the paint is discharged outside atomizingly from the peripheral edge, the particle size of the paint is not uniform, thereby deteriorating the quality of coating.
When the hardness of pigment included in the paint is high, the specific parts of the inner peripheral surface of the rotary atomizing head on which the paint moves wear out. As a result, it is difficult to lengthen the life of the rotary atomizing head.
Furthermore, the paint may be contaminated with wearing powder generated by the wearing of the rotary atomizing head and then painted on a coated surface of a coated thing so as to cause the failure of paint.
In consideration of above-mentioned circumstances, the present invention provides a rotary atomizing head that paint supplied to an inner peripheral surface is spread on the inner peripheral surface uniformly so as to improve the quality of coating and to lengthen the life of the rotary atomizing head and a rotary atomizing coating machine comprising the rotary atomizing head.